1. Field of the Invention
This invention relates to an aluminum nitride based composite body mainly composed of aluminum nitride crystal grains, an electronic functional material and electrostatic chuck employing the same, and a method of producing an aluminum nitride based composite body.
2. Description of Related Art
At present, an electrostatic chuck is used for attracting and holding a semiconductor wafer in film forming processes for the semiconductor wafer such as transportation, light exposure, chemical vapor deposition (CVD), sputtering and the like, or steps of micro-machining, cleaning, etching, dicing and the like. As a substrate for the electrostatic chuck, dense ceramics have been watched. Particularly, a halogenous corrosive gas such as ClF.sub.3 or the like is frequently used as an etching gas or a cleaning gas in an apparatus for the manufacture of the semiconductor. A dense aluminum nitride has a high corrosion resistance against the above halogenous corrosive gas. And also, the aluminum nitride is known to be a high thermal conductive material and to be high in the thermal shock resistance. Therefore, it is considered that it is preferable to make the substrate of the electrostatic chuck for a semiconductor manufacturing apparatus from an aluminum nitride sintered body.
In general, when the aluminum nitride is used as a substrate material for the electrostatic chuck, it is preferable that a volume resistivity is within a range of 10.sup.8 -10.sup.13 .OMEGA..multidot.cm at operating temperatures. However, the volume resistivity of aluminum nitride extremely decreases, for example, from 10.sup.16 .OMEGA..multidot.cm to 10.sup.7 .OMEGA..multidot.cm over a range of from room temperature to 600.degree. C., so that it is impossible to stably develop the operation as an electric chuck in such a wide temperature range. Therefore, a service temperature of the electrostatic chuck is limited to a range of, for example, 200-400.degree. C.